Available online at www.sciencedirect.com Gondwana Research 14 (2008) 277–283 www.elsevier.com/locate/gr Origin, diversification, and relationships of Cambrian lobopods ⁎ Jianni Liu a, , Degan Shu a,b, Jian Han a, Zhifei Zhang a, Xingliang Zhang a a Early Life Institute, The Key Laboratory of Continental Dynamics, Northwest University, Xi'an, 710069, PR China b School of Earth Sciences and Resources, China University of Geosciences (Beijing), 100083, PR China Received 30 April 2007; received in revised form 25 September 2007; accepted 9 October 2007 Available online 25 October 2007 Abstract As an extinct group, the origin, diversification and relationships of Cambrian lobopods have long been one of the most hotly-debated subjects. Lobopods used to be regarded as closely related to modern onychophorans and tardigrades, but the similarities are based on the few species of Cambrian lobopods and often on a fairly general level. With the discovery of new creatures and based on new observations on fossil lobopods, we consider that Cambrian lobopods show great diversity and reveal a close relationship between Cambrian lobopods and arthropods. In addition, comparison between the dorsal spines of Cambrian lobopods and small shelly fossils suggest that Cambrian lobopods might have originated from the Meishucun radiation and diversified in the Qiongzhusi radiation. © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Cambrian lobopods; Arthropods; Small shelly fossils; Origin; Diversification 1. Introduction Conway Morris (1977) described a second lobopod, Hallucigenia sparsa (see Ramsköld and Chen, 1998, Fig. 3.1), from the The supercontinent of Rodinia is described as tectonically Burgess Shale. As the two undisputed lobopods discovered in the stable and coherent between 1000 and about 750 Ma (Hoffman, Middle Cambrian, these two taxa have been widely cited and 1991). The configuration of Rodinia has been vigorously discussed (Ramsköld, 1992; Hou and Bergström, 1995; Rams- examined by scientists around the world and numerous alternative köld and Chen, 1998; Bergström and Hou, 2001; Hou et al., 2004; models have been proposed (Yoshida et al., 2003; Maruyama Zhang and Aldridge, 2007). et al., 2007). It is generally accepted that the Laurentian, Baltica, Since the Lower Cambrian Chengjiang fauna was discov- Siberia and Gondwana blocks were certainly separated by the ered in 1984 (Hou et al., 1991), Hou et al. have described split-up of Rodinia in the Neoproterozoic and moving apart six species of lobopods before the end of last century, during the Ediacaran–Early Cambrian interval (McKerrow et al., they are Microdictyon sinicum (Fig. 1a) Chen et Hou 1992). The geographic distribution of lobopods in the Cambrian 1989; Luolishania longicruris (Fig. 1i) Hou et Chen 1989; including south China, Siberia, Greenland and North America, Onychodictyon ferox (Fig. 1d) Hou, Ramsköld et Bergström indicates that this type of faunal community had dispersed 1991; Cardiodictyon catenulum (Fig. 1b) Hou, Ramsköld et worldwide in the interval from the Late Tommotian through the Bergström, 1991; Hallucigenia fortis (Fig. 1c) Hou et Atdabanian. The first lobopod to be described from the Cambrian Bergström 1995 and Paucipodia inermis (Fig. 1e) Chen, was Aysheaia pedunculata (see Briggs et al., 1994, Fig. 87, 88, Zhou et Ramsköld 1995; together with the other four 89) from the Burgess Shale, named by Walcott (1911).Later, lobopods Xenusion auerswaldae (see Dzik and Krumbiegel, 1989, Fig. 1, 4) Pompeckj (1927) from the Lower Cambrian of northern Europe; Pambdelurion whittingtoni (see Budd, 1997, ⁎ Corresponding author. Early Life Institute and Department of Geology, Northwest University, 229#, Taibai Road, Xi'an, 710069, PR China. Tel.: +86 Fig. 11.3, 11.4) Budd, 1997, Kerygmachela kierkegaardi (see 29 88303706; fax: +86 29 88302128. Budd, 1993, Fig. 1, 2, 3) Budd, 1993 and Hadranax augustus (see E-mail addresses: [email protected], [email protected] (J. Liu). Budd and Peel, 1998, plate I, II and text-fig. 2) Budd and Peel, 1342-937X/$ - see front matter © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2007.10.001 278 J. Liu et al. / Gondwana Research 14 (2008) 277–283 Fig. 1. Early Cambrian lobopods from Chengjiang Fauna. a) Microdictyon sinicum ELI-JSMS0001; b) Cardiodictyon catenulum ELI-JSC0002A; c) Hallucigenia fortis ELI-JSH0007A; d) Onychodictyon ferox ELI-JSO0011A; e) Paucipodia inermis ELI-JSP0025A; f) Megadictyon cf. haikouensis Holotype ELI-JSMH008;g) Jianshanopodia decora Holotype ELI-J007; h) Miraluolishania haikouensis Holotype ELI-JSM0020A; i) Luolishania longicruris, the Camera Lucida drawing of ours. Note that the smallest units in scale bar represent 1 mm. 1998 from the Lower Cambrian of Greenland. These animals are With the new century coming, three distinct forms regarded as closely related with each other and they have certain Miraluolishania haikouensis (Fig. 1h) Liu et Shu 2004; similarities to modern onychophorans, tardigrades and arthropods Jianshanopodia decora (Fig. 1g) Liu et Shu 2006 and (Hou and Bergström, 1995; Budd, 1993, 1997). Megadictyon cf. haikouensis (Fig. 1f) Liu et Shu 2007 have been J. Liu et al. / Gondwana Research 14 (2008) 277–283 279 discovered by the Early Life Institute (abbreviated ELI) team, and (iv) as in the rare lobopod Miraluolishania, each appendage adding significant data to the group. This is not only because of a of Facivermis bears two rows of setae on its anterior and posterior larger number of specimens and species, but in particular because margins. Besides the affinities of Facivermis with lobopods, if we these three taxa bear mosaic features of both lobopods and turn F.yunnanicus upside down and interpret the pear-shaped end arthropods. Consequently, these Cambrian lobopods are now as the anterior of F. yunnanicus rather than the posterior, it is very regarded as the intermediate creatures between lobopods and similar to the pear-shaped anterior proboscis of priapulid arthropods (Xiao, 2004; Liu et al., 2004, 2006a, 2007). Xishania longiusula (Hu, 2001). The similarities are: (i) the The possible origin of the extinct lobopods has rarely been same ratio of width/length, about 1/20; (ii) the pear-shaped discussed (Dzik and Krumbiegel, 1989; Budd, 2001a,b). Dzik anterior proboscis; (iii) two or three circles of hooks which are and Krumbiegel (1989) suggested an origin from priapulid– located in the same place; (iv) the anterior projection of proboscis; palaeoscolecid-like worms through the development of seg- (v) the clear annulations and thin spines of the body. Furthermore, ments and limbs with, at the same time, a change in the mode of the mode of life of F. yunnanicus is intermediate between life from priapulid-style burrowing within the bottom sediment burrowing and crawling. We think that most part of the body of to the crawling on the sea bottom of lobopods. Budd also F. yunnanicus rested in the sediment, and that the anterior body discussed the relationship of Cycloneuralia, lobopods and and appendages protruded out above the sea floor to catch prey. Euarthropoda based on the segmentation and Ecdysozoa concept And in terms of the posterior morphology of Facivermis,we (Budd, 2001a,b). Although both hypotheses offer hope that conceive that the enlarged pear-shaped trunk ends with two or lobopods have a close relationship with priapulid–palaeoscole- three circles of hooks could have helped to fix the animal like an cid-like worms, no intermediate creatures have been discovered to anchor of a ship when it protruded the five pairs of appendages support this idea. Fortunately, the discovery of complete specimens and made purchase to allow it to prey upon its victim. of Facivermis yunnanicus gives direct fossil evidence for this As noted above, there are certain taxa of small shelly fossils hypothesis (Liu et al., 2006b). F.yunnanicus, not only possesses the such as Microdictyon that are now regarded as lobopod plates. characters of a priapulid, but also bears features typical of lobopods. One of these, Zhijinites,asQian et al. (2000) indicated, has features ThemodeoflifeofF. yunnanicus is also just between burrowing in common with the plates and spines of both Hallucigenia and crawling. Therefore, we considered that lobopods might have (Conway Morris, 1977)andOnychodictyon (Ramsköld and Hou, originated from priapulid–palaeoscolecid-like worms. Besides, 1991). These similarities include: (1) in gross morphology, both there are some lobopod plates discovered from the Meishucun structures are composed of a sub-round plate as a base and a spine; Stage of Cambrian, such as Zhijinites (Qian, 1984, 1989)and (2) as with Zhijinites, the outer surface of spines of Hallucigenia Cambroclavus (Qian, 1984, 1989), which are probably the plates of are finely granulated; (3) especially, there usually occurs in the lobopods (Qian et al., 2000). And the similarity between small same number and symmetry of plates in one sample, and this shelly fossils and lobopods plates are hotly discussed these years situation is in accord with those of dorsal spines of Hallucigenia (Dzik, 2003; Hou and Aldridge, 2007). Thus, we suggest that the and Onychodictyon. Therefore, we are inclined to regard Zhijinites lobopods originate as early as the Meishucun radiation or even in as likely isolated dorsal plates of lobopods; if accepted, then there is the Precambrian and then diversify in the Cambrian. evidence that lobopods originated during or before the early Meis- hucun Stage. 2. Origin of lobopods 3. Diversification As noted above, the origin of lobopods is still obscure. Dzik and Krumbiegel's (1989) hypothesis of an origin from During the last few years, data on the range of Lower Cambrian priapulid–palaeoscolecid-like worms through the development lobopods has been greatly increased (Budd, 1993, 1997; Hou and of segments and limbs is the main contender. In lobopod Bergström, 1995; Budd and Peel, 1998; Ramsköld and Chen, evolution, whatever the origin, the mode of life changed from 1998; Liu et al., 2004, 2006a, 2007), while a few additional Middle priapulid burrowing to lobopod-style crawling.